The thicker a steak is, the juicier it will be. It's all about surface area, because this is where the moisture in the meat can evaporate. While a thicker steak may take a little longer to cook, you'll find the results are always worth it. You can share one thick and juicy steak between two people, rather than serving each person a thin, dry one.
The right cut
Don't let anyone tell you that you can't have your steak cooked the way you like it. After all, it's your dinner, not anyone else's. That said, for best results, if you like a rarer result, choose a lean cut such as eye fillet or rump. If you like it well done, opt for a marbled cut such as rib-eye on the bone or Scotch fillet. Sirloin is a good all-rounder.
This is something that is almost always overlooked. The closer the meat is to room temperature when it is cooked, the shorter the cooking time will be. You'll also achieve better caramelisation. A short cooking time is key to a juicy steak, as it reduces the amount of moisture evaporation.
Make sure you use the grill and not the hotplate. Your grill should be as hot as possible to allow the minimum amount of cooking time, which will help you achieve the result you're after. Remember, it's time on the grill that dries out a steak.
It's also important not to use more than half the cooking surface area at any one time. You need to be able to turn each steak onto a new hot surface, rather than a surface that's already had its heat drained by the meat.
Regardless of what you might hear from your mates at the weekend barbecue, the traditional Australian one-turn technique for cooking steak - that is, cook it on one side until the juices begin to pool, then flip it over briefly - is completely wrong. Turning often ensures even heat distribution and drives the evaporating moisture back towards the centre of the steak.
For the best results, resting meat is essential. It allows the tight muscle fibres to relax a little, which gives the meat a more tender texture. Simply set the meat aside in a warm (but not hot) place for a quarter of whatever the cooking time was, then serve. Resting the meat also means you won't end up with a pool of juices on your plate, as they will have been drawn back into the steak.